Abscisic Acid Increases Arabidopsis ABI5 Transcription Factor Levels by Promoting KEG E3 Ligase Self-Ubiquitination and Proteasomal Degradation
Abscisic Acid Increases Arabidopsis ABI5 Transcription Factor Levels by Promoting KEG E3 Ligase Self-Ubiquitination and Proteasomal Degradation
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DOI：
10.1105/tpc.110.076075
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发表时间：
2010-08-01
期刊：
影响因子：
11.6
通讯作者：
Stone, Sophia L.
中科院分区：
文献类型：
--
作者：
Liu, Hongxia;Stone, Sophia L.
拟南芥RING型E3连接酶KEEP ON GOING（KEG）是脱落酸（阿坝）信号转导的负调控因子。KEG中T-DNA插入纯合子的幼苗积累了高水平的ABA反应性转录因子ABSCISIC ACID-INSENSITIVE 5（ABI 5）。在这里，我们证明，KEG E3连接酶活性是必需的ABI 5丰度的调节。KEG在体外泛素化ABI 5，并且需要功能性KEG RING结构域来将小桶-1中的ABI 5水平恢复到野生型的水平。KEG的过表达导致阿坝不敏感性，这与KEG蛋白水平相关。在阿坝的存在下，ABI 5水平通过泛素介导的蛋白酶体降解的减少而急剧增加。我们的研究结果表明，阿坝通过诱导KEG的泛素化和蛋白酶体降解来促进ABI 5的积累。ABA诱导的KEG降解需要一个功能性RING结构域，这表明这种损失是由于自我遍在化造成的。KEG的激酶结构域内的突变或激酶抑制剂的治疗禁止ABA诱导的泛素化和降解的KEG，表明磷酸化，可能自我磷酸化，参与阿坝调节KEG蛋白水平。我们讨论了阿坝如何负调节KEG蛋白丰度，导致ABI 5和ABA依赖的细胞反应的积累的模型。
The Arabidopsis thaliana RING-type E3 ligase KEEP ON GOING (KEG) is a negative regulator of abscisic acid (ABA) signaling. Seedlings homozygous for T-DNA insertions in KEG accumulate high levels of the ABA-responsive transcription factor ABSCISIC ACID-INSENSITIVE5 (ABI5). Here, we demonstrate that KEG E3 ligase activity is required for the regulation of ABI5 abundance. KEG ubiquitinates ABI5 in vitro, and a functional KEG RING domain is required to restore the levels of ABI5 in keg-1 to that of the wild type. Overexpression of KEG leads to ABA insensitivity, which correlates with KEG protein levels. In the presence of ABA, ABI5 levels increase drastically via a decrease in ubiquitin-meditated proteasomal degradation. Our results indicate that ABA promotes ABI5 accumulation by inducing the ubiquitination and proteasomal degradation of KEG. A functional RING domain is required for the ABA-induced degradation of KEG, suggesting that the loss is due to self-ubiquitination. Mutations within KEG's kinase domain or treatments with kinase inhibitors prohibit the ABA-induced ubiquitination and degradation of KEG, indicating that phosphorylation, possibly self-phosphorylation, is involved in the ABA regulation of KEG protein levels. We discuss a model for how ABA may negatively regulate KEG protein abundance, leading to accumulation of ABI5 and ABA-dependent cellular responses.